1. Field of the Invention
The present invention relates generally to a fan system, and more particularly to a fan active noise self-lowering system, which can actively lower the noise through the fan itself and is manufactured at lower cost.
2. Description of the Related Art
Nowadays, computers have become daily used electronic devices. Most of the computers process a lot of data everyday. When processing these data, the central processing unit (CPU) in the computer will inevitably generate high heat. The high heat must be dissipated in time. Otherwise, the operation of the central processing unit will become unstable and the computer is likely to malfunction or even crash. In some more serious cases, the internal electronic components of the computer may burn down. In general, a cooling fan is used to forcedly dissipate the heat of the electronic components of the computer, (such as the central processing unit, graphic chip, Southbridge chip and Northbridge chip) so as to stabilize the operation of the computer. The cooling fan solves the heat dissipation problem of the computer. However, the fan leads to another problem. That is, in operation, the fan will make troublesome noise.
The manufacturers have more and more stressed the noise problem. This is because the noise made by the fan will cause anxiety of a user to different extents and increase tiredness of the user. As a result, the working efficiency of the user will be deteriorated. In some more serious cases, the user may be mentally and physiologically hurt. Therefore, it is academically meaningful to effectively eliminate the noise. Also, it is industrially practical to eliminate the noise so as to improve the daily life of people. In general, the conventional fan active noise control is achieved by one or more pickup microphones for capturing the noise made by the fan and generating a noise input signal to a digital signal processor (DSP). The digital signal processor receives the noise input signal and processes the noise input signal to output a control signal to one or more loud speakers for driving the speakers to emit reverse sonic wave (or so-called reverse sound source) to offset the noise.
The conventional fan active noise control can offset the noise made by the fan. However, another problem exists in the conventional device. That is, the reverse sonic wave emitted from the speakers will reflect in the environmental space to overlap the environmental noise. Therefore, the pickup microphone not only will capture the noise of the fan, but also will capture the reflective sonic wave. As a result, the noise input signal received by the digital signal processor contains the noise of the fan as well as the overlapping environmental noise and reflective sonic wave. Therefore, the operation of the digital signal processor is complicated and it is hard for the digital signal processor to generate an effective reverse sonic wave for offsetting the noise of the fan and the overlapping environmental noise and reflective sonic wave. Accordingly, the noise-lowering effect is poor and the cost for the equipment is quite high. Therefore, the conventional fan active noise control can only offset the noise made in a position where the pickup microphone is positioned.
According to the above, the conventional device has the following shortcomings:
1. The noise-lowering effect is poor.
2. The cost for the equipment is quite high.